Lens wafer with removable coating

ABSTRACT

Disclosed is a lens wafer suitable for use in preparing a laminated lens which wafer has a coating on at least one surface thereof in the form of a peelable protective film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to lens wafers and more particularly to a polymercomposition for coating at least one surface of the lens wafers in orderto provide a means to clean the wafer as well as to form a protectiveand removable film thereon.

2. State of the Art

Eyeglass lenses have traditionally been formed as a single integral bodyof glass or plastic. Grinding or molding such lenses to meet thespecifications of a particular prescription requires costly equipment,highly skilled technicians and is time consuming.

It has recently been found that the fabrication of ophthalmic lenses canbe economically accomplished in a more rapid manner with a laminatedlens construction in which two lens wafers are bonded together with atransparent adhesive. Such lens wafers are described, for example, inU.S. Pat. Nos. 5,149,181, 4,857,553, and 4,645,317 and British PatentApplication, publication number 2,260,937A which are incorporated hereinby reference in their entirety.

The laminate construction enables assembly of composite lenses havingany of a large number of different combinations of optical correctionsfrom a relatively small stock of prefabricated lens wafers of differentconfigurations. Pairing of different combinations of a front surfacelens wafer with a back surface lens wafer can, for example, providecomposite lenses having any of a large number of different powers as thepower of the lens is the summation of the powers of the two wafers. Suchcombinations provide for a large majority of all of the prescriptionsrequired for clear vision.

Notwithstanding the advantages of using lens wafers in the constructionof a composite lens, a problem arises with the use of such lens wafers.Specifically, any contaminates such as dust, dirt, fingerprints andmoisture found on the wafer surfaces to be glued will become permanentlyentrapped at the interface of the wafers in the composite lens uponadhesion of the front wafer to the back wafer resulting in defects inthe lens. These defects reduce the optical quality of the finished lensand can ultimately lead to lens rejection.

Accordingly, in order to provide a defect-free composite lens, the wafersurfaces to be laminated together (with a transparent adhesive) shouldbe substantially clean of such contaminates. However, since the wafersare invariably handled during composite lens fabrication, it isparticularly difficult to avoid contaminates such as fingerprints anddust on the wafer surface interface.

The ability to maintain a contaminant-free surface is also critical ifoptical coatings such as anti-reflection coatings are to be applied.Again, any surface damage or contamination will be uncorrectable afterapplication of the optical coating.

Previous methods known in the art neither address nor are applicable tothis problem. For example, U.S. Pat. Nos. 3,899,315 and 3,899,314 relateto texture control of glass ophthalmic lenses by use of a protectivelayer which is removed prior to use. Here, a flat glass lens preform isprovided with a thin protective layer of a chemically soluble glassfused thereto. In the manufacturing process, the flat preform issubsequently cut and pressed or slumped to the desired ophthalmic shapeand the protective layer subsequently removed by dissolving this in acorrosive reagent, thereby exposing the underlying surface which, whilesmooth, nevertheless needs to be cleaned. The lens is renderedimmediately adaptable to ophthalmic use, without further working(grinding, polishing or cleaning) of the surface. This wet process,however, is not suitable for reagent sensitive molded plastic (e.g.,polycarbonates or polymethacrylates) lenses. Furthermore, it has beenfound that the wet process does not provide a sufficiently clean surfaceon lens wafers required for laminated ophthalmic lenses.

Another unrelated prior art approach to removing dust and grease from apolymer surface is disclosed in U.S. Pat. No. 4,199,375 which describesa method for removing dust and grease from phonograph records byapplying a polyvinyl alcohol composition which forms a self-supportingfilm upon drying. When the film is lifted from the record, dust andgrease, which are dissolved in the film, are removed. However, thiscomposition, when applied to plastic lenses or lens wafers, forms filmsthat are difficult to remove.

In view of the above, it would be particularly desirable to provide ameans to effectively clean the surface of lens wafers prior to adheringthis surface to another surface during fabrication of a laminated lensor application of a coating (e.g., an anti-reflection coating) to thewafer surface.

SUMMARY OF THE INVENTION

This invention is based, in part, on the discovery that formation of aself-supporting removable film on the surface of a plastic lens waferwhich does not cross-link to the wafer surface provides an effectivemethod to clean the surface of the lens. Additionally, the removablefilm provides a level of abrasion protection to the underlying surface.

Accordingly, in one of its method aspects, this invention is directed toa method of cleaning at least one surface of a lens wafer fromcontaminates which method comprises:

(a) applying a film forming composition onto at least one surface of alens wafer, said composition comprising:

(i) a film forming unmodified polymer, and

(ii) a compatible solvent;

(b) removing the solvent from said composition to form a self-supportingremovable film that coats the surface of the wafer to which it wasapplied without being cross-linked thereto which film encapsulatestherein at least a portion of the contaminates found on the wafersurface prior to application of the composition thereto; and

(c) removing said film from the surface of the wafer.

In another of its method aspects, this invention is directed to a methodfor reducing defects at the interface of front and back lens wafers in alaminated lens wherein the front and back lens wafers are bondedtogether at the surfaces interfacing with each other with a transparentadhesive which method comprises:

(a) applying a film forming composition onto the interface surfaces ofboth the front and back lens wafers, said composition comprising:

(i) a film forming unmodified polymer; and

(ii) a compatible solvent;

(b) removing said solvent to form a self-supporting removable film thatcoats the surface of the wafer to which it was applied without beingcross-linked thereto which film encapsulates therein at least a portionof the contaminates found on the wafer surface prior to application ofthe composition thereto;

(c) removing said film from the surface of the wafer;

(d) applying a transparent adhesive to at least one of said interfacesurfaces; and

(e) bonding the front lens wafers to the back lens wafer through theinterface surfaces of said wafers to form a laminated lens.

In one of its composition aspects, this invention is directed to a lenswafer suitable for use in preparing a laminated lens, said wafercontaining on at least one surface thereof a self-supporting removablefilm wherein said film is not cross-linked to said wafer surface andfurther wherein said film encapsulates at least a portion of thecontaminates found on the lens surface prior to placement of said filmthereon.

Upon removal of the film from the lens wafer surface, the contaminatesencapsulated with the film are removed from this surface. Preferably,the film has a thickness, in the dry state (after solvent evaporation),of from about 8 to about 50 μm (microns), more preferably from about 8to about 20 μm, and still more preferably from about 10 to 15 μm.

In another of its composition aspects, this invention is directed to alens wafer suitable for use in preparing a laminated lens said wafercontaining on at least one surface thereof a self-supporting removablefilm wherein said film is prepared by the process which comprises:

(a) applying a film forming composition onto a surface of the lenswafer, said composition comprising:

(i) a film forming unmodified polymer; and

(ii) a compatible solvent; and

(b) removing said solvent to form the removable film that coats thesurface without being cross-linked thereto.

In a preferred embodiment, the film forming unmodified polymer comprisesa copolymer of vinyl chloride and vinyl acetate. More preferably, thecopolymer of vinyl chloride and vinyl acetate comprises from about 75 toabout 98 weight percent vinyl chloride and from about 2 to about 25weight percent vinyl acetate. In still a more preferred embodiment, suchcopolymers have a molecular weight of from about 15,000 to about 70,000.

In still another preferred embodiment, the polymer composition furthercomprises a second copolymer of vinyl chloride and vinyl acetate thathas an average molecular weight of about 40,000 to 50,000 wherein thesecond copolymer comprises about 80 to 90 weight percent vinyl chlorideand about 10 to 20 weight percent vinyl acetate. The polymer compositioncomprising the first and second copolymers preferably has a weight ratioof the first copolymer to the second copolymer of from about 8:1 toabout 19:1. A particularly preferred polymer composition comprises about94 weight percent of the first copolymer and about 6 weight percent ofthe second copolymer.

In yet another composition aspect, this invention is directed to acomposition comprising:

(1) from about 60 to about 95 weight percent, based on the total weightof the composition, of a solvent mixture comprising acetone and n-amylacetate as the compatible solvent;

(2) from about 5 to about 25 weight percent, based on the total weightof the composition, of a film forming unmodified polymer;

(3) from about 10 to about 35 weight percent, based on the total weightof solids in the film forming composition, of a plasticizer comprisingdipropylene glycol dibenzoate; and

(4) from about 0.1 to about 5 weight percent, based on the weight of thecomposition, of an anti-static agent.

In another of its compositional aspects, the invention is directed to acomposition suitable for forming a self-supporting removable polymericfilm on at least one surface of a lens wafer suitable for forming acomposite lens which composition comprises:

(a) a first copolymer that comprises from about 75 to 98 weight percentvinyl chloride and about 2 to 25 weight percent vinyl acetate and thathas an average molecular weight of about 25,000 to 28,000;

(b) a second copolymer that comprises about 80 to 90 weight percentvinyl chloride and about 10 to 20 weight percent vinyl acetate and thathas an average molecular weight of about 40,000 to 50,000

wherein the weight ratio of said first copolymer to said secondcopolymer ranges from about 8:1 to about 19:1; and

(c) a compatible solvent.

Preferably, the compatible solvent is selected from the group consistingof acetone, ethyl acetate, amyl acetate, butyl acetate, and mixturesthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exploded laminated lens comprising a front lenswafer, a transparent adhesive layer and a rear lens wafer.

FIG. 2 illustrates the laminated lens of FIG. 1 in combined form whichlens is suitable for use in corrective glasses.

DETAILED DESCRIPTION OF THE INVENTION

This invention is directed to methods and compositions for cleaning lenswafers for use in preparing optically corrective laminated plasticlenses. The methods and compositions of this invention employ aself-supporting removable film on at least one surface of the waferwhich film is not cross-linked to the wafer but which film encapsulatestherein at least a portion of the contaminates found on the surface ofthe lens wafer.

However, prior to addressing this invention in further detail, thefollowing terms will first be defined:

Definitions

The term "lens wafer" or "wafer" refers to an article comprising aplastic material which article is either the front or back segment of acomposite lens which segments are combined and bonded together by use ofa transparent adhesive. Such lens wafers are depicted in FIG. 1 aselements 10 and 14. Plastic materials useful in preparation of lenswafers are well known in the art and include, by way of example,polycarbonates, polymethacrylates, and the like. The particular plasticmaterial employed is not critical. However, preferred plastic materialsare polycarbonates and, in particular, an allyl diglycol carbonateavailable from PPG Industries, Hartford, Conn., U.S.A. under thetradename CR-39™.

The term "transparent adhesives" refers to adhesives suitable forbonding lens wafers together which adhesives are optically transparentin the visible light portion of the spectrum and preferably UV curable.Such transparent adhesives are disclosed in U.S. Pat. Nos. 5,149,181,4,857,553, and 4,645,317 and British Patent Application, publicationnumber 2,260,937A. The particular transparent adhesive employed hereinis not critical but preferably is a UV curable adhesive sold under thetradename MULTI-CURE 492 available from Dymax, Inc., Torrington, Conn.,U.S.A.

The term "a film-forming unmodified polymer" refers to a polymer ormixture of polymers, including copolymers, that are soluble orsuspendable in a compatible solvent such that upon removal of thesolvent a film is formed on the surface to which the polymer solution orsuspension was applied and which polymers do not contain sufficientfunctional groups (and preferably no functional groups) so as to resultin cross-linking of the polymer to the lens wafer surface. Cross-linkingof the polymer to the lens wafer surface refers to covalent or ionicbinding of functional groups on the polymer to complementary functionalgroups found on the surface of the wafer. Such binding (cross-linking)is particularly detrimental since it inhibits the ability to lift theresulting film off the wafer to leave a clean surface (e.g., withoutleaving traces of the polymer) without deleteriously affecting thesurface of the lens wafer.

Generally, unmodified polymers do not have sufficient reactive moieties,such as hydroxyl, carboxyl, epoxy, or amino functionalities, that couldbind (cross-link) with complementary reactive functionalities on thesubstrate surface thereby forming a covalent or ionic linkagetherebetween. For example, it is believed that the hydroxylfunctionality will readily cross-ink with plastic substrates by formingester and/or ether bonds with complementary reactive groups on the wafersurface (e.g., carboxyl groups and epoxide groups).

Preferred film forming unmodified polymers have a number averagemolecular weight of from about 15,000 to about 70,000, preferably 20,000to 45,000 and most preferably from about 25,000 to about 28,000. The useof polymers having lower molecular weights facilitates the preparationof high solid content solutions of these polymers in the compatiblesolvent. High solid contents are particularly desirable in areas wheresolvent emissions are restricted on the basis that solvent coatingtechniques are limited to high solid contents.

In a particularly preferred embodiment, the film forming unmodifiedpolymer comprises a copolymer of vinyl chloride and vinyl acetate. Morepreferably, the copolymer of vinyl chloride and vinyl acetate comprisesfrom about 75 to about 98 weight percent vinyl chloride and from about 2to about 25 weight percent vinyl acetate. In still a more preferredembodiment, such copolymers have a number average molecular weight offrom about 25,000 to about 28,000.

In still another preferred embodiment, the polymer composition furthercomprises a second copolymer of vinyl chloride and vinyl acetate thathas an average molecular weight of about 40,000 to 50,000 wherein thesecond copolymer comprises about 80 to 90 weight percent vinyl chlorideand about 10 to 20 weight percent vinyl acetate. The polymer compositioncomprising the first and second copolymers preferably has a weight ratioof the first copolymer to the second copolymer of from about 8:1 toabout 19:1. A particularly preferred polymer composition comprises fromabout 94 weight percent of the first copolymer and about 6 weightpercent of the second copolymer.

It has been found that the presence of such a second unmodified polymerin the polymer composition produces films with enhanced physicalcharacteristics such as increased tensile properties which facilitatethe stripping of the film from the substrate. Specifically, the additionof this second unmodified polymer having a higher average molecularweight than that of the first improves the physical properties of thefilm.

When the unmodified polymer comprises vinyl resins such as copolymers ofvinyl chloride and vinyl acetate, a preferred solvent comprises amixture of acetone and n-amyl acetate. The acetone is present from about60 weight percent to 100 weight percent, and preferably at about 95weight percent of total solvent; the n-amyl acetate is present from 0weight percent to about 40 weight percent, preferably from about 1 toabout 5 weight percent and still more preferably at about 5 weightpercent of total solvent. This solvent mixture has the advantage ofdissolving the vinyl copolymer at room temperature. The n-amyl acetate,which is a slow-evaporating solvent, facilitates application of thecomposition to lens substrates and, in particular, allows thecomposition to flow over the substrate to achieve a uniform coating.

The term "compatible solvent" refers to a solvent or mixture of solventswhich dissolve or suspend the film forming unmodified polymer(s) andother components of the polymer composition which solvent is notdeleterious to the surface of the lens wafer. Solvents should besufficiently volatile so that once the polymer composition is appliedonto a substrate surface, the solvent can be removed to form the filmpreferably without the aid of heat and/or vacuum. Additionally, thesolvent should preferably have a solvent cleaning affect on the surfaceof the lens wafer such that at least a portion of the contaminants foundon the surface of the lens are dissolved or suspended in the solution(i.e., solvent+film-forming unmodified polymer). Preferred solventsinclude acetone, ethyl acetate, amyl acetate, butyl acetate, etc., andmixtures thereof.

The term "self-supporting removable film" refers to a polymer filmhaving sufficient tensile strength and modulus such that the filmstability (i.e., in a stable film form) is independent of the lens wafersurface to which it is applied and which film does not cross-link withthe wafer surface thereby permitting complete peeling therefrom,preferably as a single piece.

The term "contaminants" refer to exogenous materials found on theinterface surface of a lens wafer which can become entrapped at theinterface of the wafers in a laminated lens resulting in defects to thelens. Such contaminants include, by way of example, dust, dirt,fingerprints (including oils associated therewith), moisture, etc.

Formulation

This invention is directed to the discovery that the formation of aself-supporting removable film on the surface of the lens wafer providesan effective means to dissolve and/or encapsulate at least a portion ofthe contaminants on the surface of the film. Upon removal of the filmfrom the lens wafer surface, the contaminates dissolved and/orencapsulated within the film are removed from this surface. The filmprovides the additional advantage of protection from abrasion for thesurfaces of the wafer covered by the film.

Specifically, FIG. 1 is an exploded view of the elements used to producea laminated lens 1. Transparent adhesive layer 12 is used to bond thefront lens wafer 10 to rear lens wafer 14. Viewing the lens from left toright, the rear surface 16 of front lens wafer 10 and the front surface18 of rear lens wafer 14 are the interface surfaces for each wafer inthe bonded lens. FIG. 2 illustrates the composite (laminated) lens 1 inassembled form.

In this invention, it is desirable to clean at least a portion of thecontaminants on the interface surfaces 16 and 18 of front and backwafers 10 and 14 respectively prior to bonding these wafers togetherwith the transparent adhesive layer 12. Specifically, cleaning isaccomplished by first applying a composition comprising a solventsolution or suspension of a film forming unmodified polymer that forms aself-supporting and removable film when applied to the surface of theplastic lens wafer, subsequent removal of the solvent to form theremovable film and then, at some point in time subsequent thereto,removal of the film.

In this composition, the compatible solvent is typically employed in anamount of from about 60 to about 95 weight percent of the total weightof the film-forming composition and preferably from about 70 to about 80weight percent. The use of lower amounts of compatible solvent ispreferred when emission of solvent to the atmosphere is of concern. Thefilm forming unmodified polymer is employed in this composition in anamount of from about 5 to about 25 weight percent, based on the totalweight of the composition, and preferably from about 15 to about 23weight percent.

In a preferred embodiment, the polymer employed in the film formingcomposition comprises a copolymer comprising about 86 percent vinylchloride and 14 percent vinyl acetate and having an average molecularweight of about 27,000. In another embodiment, the polymer composition,further comprises a second copolymer comprising about 90 percent vinylchloride and 10 percent vinyl acetate and having an average molecularweight of about 44,000. The second copolymer is preferably present atfrom 5 to 20 percent by weight of total copolymer.

The film forming composition described above can optionally containadditives such as anti-static agents, plasticizers, anti-oxidants, etc.Plasticizers are typically employed to improve film flexibility andpeelability and, when employed, are present at from about 20 percent toabout 30 percent by weight based on total solids (i.e., exclusive ofsolvent) content. Suitable plasticizers include, by way of example,dipropylene glycol dibenzoate, butyl benzyl phthalate, diethylene glycoldibenzoate, and the like. The particular plasticizer employed is notcritical but preferably is dipropylene glycol dibenzoate.

Anti-static agents are typically employed to reduce the amount of staticcharge created especially when peeling the film from the composite lens.When employed, the composition comprises from about 0.1 to about 5weight percent of the anti-static agent based on the total weight of thecomposition and preferably about 1.5 weight percent. Suitableanti-static agents include, by way of example, Glycolube AFA™ (availablefrom Lonza, Inc., Fair Lawn, N.J., U.S.A.), glycerol monooleate,polyoxyethylene sorbitan monooleate, and the like. Alternatively, afterpeeling the removable film from the wafer surface, the wafer surface canbe exposed to a bipolar ionized air shower to reduce static.

The above composition is preferably prepared by the addition of the filmforming unmodified polymer to the compatible solvent. The rate ofaddition is monitored and maintained at a sufficiently slow rate toinhibit lumping of the polymer. Mixing is conventionally conducted in ahigh shear mixer preferably equipped with a tight fitting cover toprevent solvent loss.

Methodology

In operation, the film forming composition prepared as above is appliedto at least one surface of lens wafer suitable for forming a compositelens. Preferably, the film forming composition is applied to theinterface surface of both the front and back lens wafers. In oneembodiment, the film forming composition is applied only to theinterface surfaces of both the front and back lens wafers. In anotherembodiment, the film forming composition is applied to all of thesurfaces of the lens wafer.

Application is typically conducted in a manner to provide substantiallyuniform application of the film forming composition onto the lens wafersurface. Application means include, by way of example, roll coating, dipcoating, painting, spin coating, etc. Application by a spin coatingprocess gives an upper thickness limit of about 20 μm.

In some cases it may be desirable to add solvent to the film-formingcomposition during active coating of the wafer surface to maintain thedesired solvent level. Solvent addition can be either incremental orcontinuous and compensates for solvent loss during coating.

Sufficient amounts of the film forming composition are applied onto thesurface or surfaces of the lens wafer to provide for a film thickness,in the dry state (after solvent evaporation), of from about 8 to about50 μm (microns), more preferably from about 8 to about 20 μm, and stillmore preferably from about 10 to 15 μm. Film thickness of at least 8 μmis necessary to insure that the film is strong enough to exhibit goodpeelability. As is apparent, a thicker film will also afford greaterabrasion resistance.

The coating should be coextensive with the surface(s) of the lens waferso that after solvent removal, a film is formed which is closelyjuxtaposed to the wafer surface and remains attached until it is peeledoff and the lens wafer is ready for use. Accordingly, attachment is madeby proximate location of the film coextensive with the surface of thewafer. There is, however, no chemical binding, whether covalent orionic, between the film and the wafer and, accordingly, the film ispeelable.

The methodology employed to form the film results in a cleaning effecton the wafer surface upon removal of the film. Without being limited toany theory, it is believed that the solvent employed in the film formingcomposition suspends or dissolves a portion of the contaminants whenapplied to the surface of the wafer. Upon evaporation of the solvent,the contaminants are believed to become encapsulated in the film and,upon film removal, a cleaning effect of the wafer surface is achieved.

In addition to cleaning the wafer surface, the removable film alsoprovides abrasion protection for the surface to which it was applied.Accordingly, it is advantageous to form the removable film on at leastone surface of the wafer at the time of manufacture and remove the filmat the time of forming the corrective lens thereupon retaining this filmon the surface of the wafer during shipment and storage. However, whileless advantageous, this invention also encompasses application of thefilm to the lens wafer surface immediately prior to forming thecorrective lens so as to effectively clean the lens surface prior tolamination. In this embodiment, it may be desirable to repeatapplication and removal of the film to the surface to provide for higherlevels of cleaning.

It is contemplated that the self supported removable film describedabove can also be employed to clean the surface of any plastic lens,regardless of whether the lens is of laminate construction. Suchcleaning would be required prior to, for example, application of ananti-reflective coating to the lens. In this embodiment, the lens isfirst cleaned in the manner described above and then treated with theanti-reflective coating. The cleaning step prior to application of theanti-reflective coating ensure that contaminates on the lens surface arenot permanently entrapped into the lens/anti-reflective coatinginterface. All of the parameters discussed above relating to cleaning oflens wafers would be applicable to the cleaning of the lens itself.

Embodiments of the invention are now described by way of the followingnon-limiting examples.

In these examples, the following abbreviations have the meanings setforth below. If not defined, the abbreviations have their art recognizedmeanings.

g=grams

min.=minutes

Mn=number average molecular weight

μm=microns (micrometers)

EXAMPLES

Example 1 describes preparation and application of a film formingunmodified composition to form a protective film on a plastic lenswafer. Example 2 describes the same technique except that the unmodifiedpolymer employed comprises of a mixture of vinyl chloride and vinylacetate copolymers. Comparative Example A describes films formed from apolymer composition wherein the vinyl chloride and vinyl acetatecopolymer has a hydroxyl content of about 2.3 percent. As is apparent,the presence of the hydroxyl groups forms a film that strongly bonds tothe substrate and therefor is unsuitable for use as a peelableprotective film.

Example 1

441 g of a copolymer of vinyl chloride and vinyl acetate havingapproximately 86 weight percent vinyl chloride and about 14 weightpercent of vinyl acetate and a number average molecular weight of about27,000 (available from Union Carbide Chemicals and Plastics Co.,Danbury, Conn., U.S.A. under the tradename UCAR Solution Vinyl ResinVYHH™) was added to a solvent blend comprising 1,330 g acetone and 70 gamyl acetate. The VYHH™ was added slowly under agitation at roomtemperature and in a sealed container in order to prevent clumping andsolvent loss. A high shear mixer was used to provide the requiredagitation. Dissolution of the copolymer required almost one hour. 150 gof a plasticizer consisting of dipropylene glycol dibenzoate (availableunder the tradename Benzoflex 9-88™ from Velzicol Chemical Corp.,Rosemont, Ill., U.S.A.) was then added to the mixture, and the mixturestirred for five minutes. This was followed by the addition of 9 g of ananti-static agent (available under the tradename Glycolube AFA-1™ fromLonza, Inc., Fair Lawn, N.J., U.S.A.). The polymer composition wasstirred for 10 min. prior to application. The composition comprisedabout 30 percent solids by weight.

Table 1 lists the components and proportions in the polymer composition.

                  TABLE 1                                                         ______________________________________                                                       WEIGHT    WEIGHT    SOLIDS                                     COMPONENT      (gram)    (percent) (percent)                                  ______________________________________                                        VYHH ™      441       22.05     73.50                                      BENZOFLEX 9-88 ™                                                                           150               7.50                                                                                 25.00                                GLYCOLUBE AFA-1 ™                                                                           9                0.45                                                                                  1.50                                ACETONE                          66.50                                                                                     0                                AMYL ACEATE                       3.50                                                                                     0                                TOTAL                              100                                                                                   100                                ______________________________________                                    

The polymer composition of Example 1 was applied to an ophthalmic lenswafer substrate formed of a polymerized allyl diglycol carbonate(available as CR-39™ PPG Industries, Hartford, Conn., U.S.A.). Thecomposition was applied by spin coating whereby the lens is mounted on arotatable spindle and rotated at a high speed to disperse the liquidover the moving surface to attain a coating of uniform thickness. Thecoating was allowed to dry at ambient conditions to form a solid film onthe lens wafer. Preferably, the film is about 10 μm thick.

The film was removed by attaching adhesive tape to an edge region of thesubstrate and withdrawing the tape from the substrate to peel the filmaway. The film exhibited good peelability and cleaning effectiveness asit was able to remove surface dust and grease-based contaminants (e.g.,fingerprints) without breaking up.

Example 2

The procedure described above in Example 1 was carried out, with thereplacement of the single VYHH™ copolymer with a mixture of VYHH™ andUCAR Solution Vinyl Resin VYNS-3™ (also available from Union CarbideChemicals and Plastics Co., Danbury, Conn., U.S.A.) which is anothervinyl chloride/vinyl acetate copolymer, which comprises about 90 percentvinyl chloride and about 10 percent vinyl acetate and has a numberaverage molecular weight Mn of about 44,000. The proportion of VYHH™ toVYNS-3™ was about 95 percent VYHH™ to 5 percent VYNS-3™, by weight.

The mixture was prepared by adding VYNS-3™ slowly to acetone underagitation for almost one hour until the VYNS-3™ dissolved. Aftercomplete dissolution of the VYNS-3™, the VYHH™ was slowly added,requiring also approximately one hour for complete dissolution.Thereafter the plasticizer and anti-static agent were added to themixture, and the final composition applied to a lens surface by spincoating. The resultant film exhibited particularly good film propertiesin terms of film tear strength and toughness.

Comparative Example A

The procedure of Example 1 was repeated but the copolymer used was avinyl chloride/vinyl acetate copolymer with vinyl alcohol in the polymerbackbone (available as VAGH™ from Union Carbide), and having a vinylchloride content of about 90 percent, about 4 percent vinyl acetate,with a hydroxyl content of about 2.3 percent and a number averagemolecular weight of about 27,000.

The film was evaluated for its strippable characteristics from a CR-39™lens wafer substrate. It was found that the film adhered strongly to thesubstrate, and could not be stripped therefrom. This is due to crosslinking with the plastics lens wafer substrate as a result of thehydroxyl functionality.

The subject matter disclosed herein is also found in our priorityBritish Patent Application No. 9403792.6 which is incorporated herein byreference in its entirety.

Although only preferred embodiments of the invention are specificallydisclosed and described above, it will be appreciated that manymodifications and variations of the present invention are possible inlight of the above teachings and within the purview of the appendedclaims without departing from the spirit and intended scope of theinvention.

What is claimed is:
 1. A lens wafer suitable for use in preparing alaminated lens said wafer containing on at least one surface thereof aself-supporting removable film which film is a vinyl resin comprising(a) a first copolymer of vinyl chloride and vinyl acetate, wherein saidfirst copolymer comprises from about 75 to about 98 weight percent ofvinyl chloride and from about 2 to about 25 weight percent vinyl acetateand further wherein said first copolymer has a number average molecularweight of from about 25,000 to about 28,000: and (b) a second copolymerof vinyl chloride and vinyl acetate, wherein said second copolymercomprises from about 80 to about 90 weight percent of vinyl chloride andfrom about 10 to about 20 weight percent vinyl acetate and furtherwherein said second copolymer has a number average molecular weight offrom about 40,000 to 50,000; and wherein the weight ratio of the firstcopolymer to the second copolymer is from about 8:1 to about 19:1;wherein said film is not cross-linked to said wafer surface and furtherwherein said film encapsulates at least a portion of the contaminantsfound on the lens surface prior to placement of said film thereon. 2.The lens wafer of claim 1 wherein the film further comprises aplasticizer.
 3. The lens wafer of claim 2 wherein the plasticizercomprises dipropylene glycol dibenzoate.
 4. The lens wafer of claim 3wherein the film further comprises an anti-static agent.
 5. The lenswafer of claim 1 wherein the film is from about 8 to about 50 μm thick.